A variety of biochemical and genetic techniques will be used to study the replication of retroviruses and some of the genes implicated in retroviral oncogenesis. In the studies on viral replication, emphasis will be placed upon receptors that mediate virus entry, the mechanism of proviral integration, synthesis of viral proteins via ribosomal frameshifting, and assembly of viral envelopes. Two classes of proto-oncogenes, the src and Wnt gene families, will be examined in efforts to understand the role of their protein products in signalling in individual cells, development in whole organisms, transformation of cultured cells, and multi-step oncogenesis in transgenic animals.